Given the most recent comments from the Russo brothers on their artistic vision when it comes to directing Avengers: Doomsday, it seems safe to say that a major effort is going into making sure the upcoming MCU movie capitalizes on its capacity to change one of the biggest movie worlds of all time forever - and thus begins a new era for the franchise that we've all been waiting for a long time to see.
When discussing the way Avengers: Doomsday's story would handle the MCU's past and future while also balancing being its own distinct entity during an appearance at SXSW London (as reported by The Hollywood Reporter), Anthony Russo explained that the intention was to approach Doomsday as a "phase zero" release, stating:
"Look, we were with Rob [Downey Jr.] earlier today. We were both talking about this concept that we are back to phase zero. This is starting over from scratch. We want to make sure everybody feels like this isn’t leaning on anything from the past."
This is promising to note given the MCU has thus far ostensibly lived more in the shadow of Avengers: Endgame directly, since almost all of its storylines have had to deal with either the direct results of Endgame and the events within it, or otherwise with the awkward configuration the franchise found itself in without the Avengers or many of the franchise's major flagship heroes to act as anchors for its various branching stories.
While it was always evident that providing a story that simultaneously builds on what came before without requiring audiences to watch almost 40 movies in order to understand what's going on would be a priority, the phase zero comment makes it clear just how much this is a priority of the filmmakers, which hopefully should mean Doomsday can work for hardened MCU veterans and newer or lapsed fans.
Excitingly, these comments about Avengers: Doomsday acting as a phase zero movie conceptually also serve to reiterate that we are in a period that will be a reboot of sorts for the MCU whatever unfolds next - with the only difference being whether that turns out to be a full-scale reboot that revamps the franchise in a more major way, or a soft reboot that simply tweaks some smaller details in a lighter manner.
Though the Russos are very unlikely to throw out all that came before, the focus on "starting over from scratch" and not leaning on the past is effectively confirmation that the MCU will be undergoing a revamp of sorts, with the focus being on paving a new path that can support the franchise as it is now, and hopefully ensure the MCU doesn't continue to live on in Endgame's shadow in quite the way it has seemed to in recent years, if only because the next era for the Avengers will have been unveiled.
As such, Avengers: Doomsday looks to be all the more important for the franchise, and may well set the stage for whatever reboot plans are in mind for Avengers: Secret Wars, which stands a better chance of concluding with some more major revamps - potentially adding further significance to the specific use of the "phase zero" term.